Expulsion-tube discharge device



Patented Nov. 11, 1941 I r I 2,262,369

EXPULSION-TUBE DISCHARGE DEVICE Alert M. Opsahl, Pittsburgh, Pa.,assignor to Westinghouse Electric & Manufacturing Company, EastPittsburgh, Pa., a corporation of Pennsylvania Application September30,1939, Serial No. 297,339 6 Claims. (01, na -30) My invention relatesto excess-voltage protector tubes of the gaseous expulsion type, for theprotection of line-insulators or apparatusinsulation againstexcess-voltage surges such as may be caused by lightning.

One of the principal objects of my invention is to devise a practicalmeans for providing a variable-width, protective discharge-path whichnected, particularly on lines having extremely small short-circuitcurrents.

In accordance with my present invention, practical means areprovided forcausing the gaseous pressures, which are built up on the slot duringeither a severe surge-discharge or a severe powerfollow current-flow, topush theslot-walls further automatically varies its widthin accordancewith the operating conditions. The discharge-path is made in the form ofa long, narrow slot, and

. izing the gas which composes the arc-path, and

hence rendering that gas less conducting or even non-conducting, and atthe same time physically aiding in the interruption of the arc bycreating a powerful gas-blast which blows the are out of theprotector-tube.

Such an excess-voltage protector-tube has two functions to perform.First, it must be capable of discharging the momentarily flowingsurgecurrent, which may be of any value ranging over an extremely widerange of values, and lasting for a very small fraction of acycle of a60-cycle' power-system. After the surgedischarge, the

protector-tube mustbe capable of interrupting the flow of the so-calledpower-follow current or follow-up current which discharges from the 60-cycle power line through the conducting gases or the arc-pathestablished by the surge-discharge, and this power-follow current mayhave any one of many different values on different power-systems,ranging from very small currents on long, rural distribution-lines, toextremely heavy currents on important or heavy-duty power-lines ofeither the transmission or distribution class.

apart so as to avoid rupture of the device, while the narrow initialvalue of the slot-vvidth enables the device to interrupt thepower-follow current on lines in which the short-circuit current is verylow. My invention is particularly useful in cases where the same type oftube may sometimes be applied on rural lines, where thelightning-discharge currents are high andof frequent occurrence but thepower-follow currents are low, and may at other times be applied onhigh-capacity power-systems, in connection with which it has heretoforebeen frequently necessary to add a resistor in series with theexcess-voltage protector tubes previously utilized, in order to limitthe bursting-effects and the erosion which occurs at the highpower-follow currents which are obtained, the resistor beingobjectionable because it weakens the ability of the tube to protect theline against high surge-voltages.

One of the objects of my invention is to provide means whereby anexpulsion-type discharge-tube has the lowest possible ratio ofdischarge-voltage to interruption-voltage, so that the tube will becapable of flashing over, undersurge-conditions which result in only asmall increase over the normal line-voltage. A low flashover voltage, or

lightning-discharge voltage, means a short internal spacing between theelectrodes, inside of the tube, as measured through the long, narrow 1discharge-slot, but when this arcing length, or

In the design of a slot-discharge protective tube,the slot cannot be toonarrow, or else the more severe of the lightning-current dischargesspacing between electrodes, gets too short, it is much more difficultfor thetube to interrupt the power-follow currents at any given voltage,In accordance with my invention, I utilize a slot which is initially ofa width corresponding to the narrowest width that would ever be desired,and

I prevent failures due to rupture of the tube by causing the width ofthe slot to be automatically increased, when occasion demands, said slot7 automatically returning to its narrower width as soon as the gaseouspressure abates in the tube, so that the maximum power-followinterruptingcharacteristics are always available. I can therefore'builda tube which has a lower ratio of flashover-voltage to line-voltage.

A more specific object of my invention is to provide a discharge-tubehaving a conically shaped opening at one end, with a conical insulatingplug in said opening, the plug being mounted for axial displacement, soas to increase the slot-width between the two conical surfaces, thisaxial displacement being resisted by a spring.

With the foregoing and other objects in view, my invention consists inthe apparatus, combinations, parts, systems and methods hereinafterdescribed and claimed, and illustrated in the accompanying drawing, thesingle figure of which is a longitudinal sectional view of an exemplaryembodiment of an excess-voltage protector-tube made in accordance withmy invention.

The particular protective tube which is illustrated in the drawingcomprises a tubular insulating member I having an opening which isconically enlarged at one end, as indicated at 2, and a conicalinsulating plug 3 in said conical opening. At least one of the conicalsurfaces preferably includes material which is capable of evolvingdeionizing gases or particles under the s influence of an arc, and inthe preferred embodiment of my invention, both the tube I and the plug 3are made of fiber, which has this property.

The non-conical end of the tube I is closed by a metal cap 4 whichcarries a centrally mounted metal or other conducting rod 5 whichconstitutes one of the arc-terminal electrodes of the device, and thisis preferably the terminal which is connected to the high-voltage lead 6which runs to the power-line or electrical apparatus to be protected.The electrode 5 has an inner end, or arc-terminal, which is centrallyhollowed, as indicated at I, so as to provide an annular, beveledelectrode-end 8 which terminates inside of the tube, adjacent to thesmall ends of the conical opening 2 and the conical plug 3.

The conical-opening end of the tube I, which is usually the lower end,is engaged by a vented metal capping-piece Ill which is of open tubularconstruction and which has an inner, annular seat or flange II, whichconstitutes the second conducting electrode of the device, said secondconducting electrode being disposed adjacent to the large ends of theaforesaid said conical opening-portion 2 and conical plug 3, asindicated at II. The end of the cap-member I0 is vented, or open to theatmosphere, and this end of the capmember I0 is also arranged tointegrally support a central cup-member I3 which is united to thetubular part of the cap-member by means of a plurality of webs orspider-arms I l. The large end of the conical plug 3 has a reducedextension I5 which extends into the top of the cup I3, and the cup I3 isfitted with a strong compressionspring IG which bears up against thebottom of the plug-extension I5 and yieldingly presses the plug in anexial direction tending to force it into the conical opening 2.

In accordance with my invention, I preferably provide spacing-means forcausing at least portions of the two conical surfaces to be separated byan initial or minimum separation or slotwidth of at least onesixty-fourth of an inch, or of anywhere from one sixty-fourth of an inchto one twenty-fourth of an inch, depending upon the design-conditions.In the illustrated form of my invention, this spacing-means takes twoforms, either or both of which can be omitted, andv either of which canbe changed so as to have other formations. One of the means forpreventing the plug 3 from being pressed too far into the conicalopening 2, by the axially directed spring I6, is a suitable abutment onthe inner terminal of the upper, electrode 5, for the small end of theplug 3. In the illustrated embodiment, this abutment takes the form of aplurality of small lugs II carried by the walls of the central hollow Iof the electrode 5. Another means for preventing the plug 3 from beingpushed too far into the conical opening 2 may take the form oflongitudinally extending ribs, or preferably short, discontinuousprojections I8, carried either by the plug 3 or the walls of the conicalopening 2, so as to properly align the plug 3 within the opening 2 01 tolimit the minimum possible slot-width between the two conical surfaces.Some adjustment of the minimum slot-width between the two conicalsurfaces may be obtained by axially ad justing the upper electrode 5, asby means of a threaded connection I9 between said electrode and theclosed cap-end 4.

In certain cases, I may also provide a special venting-means for thenormally closed electrode 5, and in the illustrated form of theinvention, this special venting-means takes the form of a long, narrow,centrally disposed opening 2|, extending through the rod-like electrode5, from the inner, arc-terminal depression I to a second hole orcup-like depression 22 which is provided at the outer end of thelectrode-rod 5, the junction between the small central hole 2I and thebottom of the cup-like depression 22 being normally closed by aspring-pressed relief-valve 23. With this construction, the plug-likeelectrode 5 is normally closed or unvented, but in case the internalgaseous pressure should become very excessive, threatening to exceed therupturing strength of the insulating tube I, this pressure can beautomatically relieved by the opening of the valve 23, thus avoiding afailure of the protective tube.

The bottom, or permanently vented, electrodemember Ill-II will, ingeneral, be the low-voltage electrode of the device, as indicated by theground-connection 24.

In operation, the high-voltage terminal-lead 6 is connected to the lineor apparatus which is to be protected by my device. In case a surge ofany sort should cause a momentary rise in the voltage which is appliedto the terminal-lead 6, a very slight increase in this voltage, over andabove the normal or rated value, will suihce to cause an internaldischarge within the tube, in the long, narrow slot between the twoconical openings, said discharge passing from one electrode-tip 8 to theother electrode-tip I I, through said slot. It is necessary that thisdischarge shall be an internal discharge, in the long, narrow slotprovided therefor, rather than an external discharge between the two endcap-pieces 4 and II], respectively, across the external discharge-spacewhich is indicated at 25, because the long, narrow internal slot betweenthe two conical surfaces, and the gas evolving wall-material of saidslot, both combine to provide good arc-interrupting characteristics soas to interrupt the resulting power-follow current, which would not bethe case in the event of an external discharge across the outside space25. It is necessary, therefore, for one or both of the arc-terminalelectrodes to extend part way into the tube I, for a sufficient totaldistance, so that the length and fiashover-voltage of the internalarcing-space between the electrode-tips 8 and II, shall be small enoughso that the discharge always takes place interiorly, rather thanexternally across the outer gap 25.

If the surge-current which is discharged by the device is small, thesurge-current flow will not develop suflicient gaseous pressures to movethe plug 3 in a radial direction against the-opposition of itscompression-spring I6. After the discharge of the current, whichconstitutes the surge, if the power-follow current is also small, it tooWill develop only a small gaseous pressure in the arcing path, so thatthe plug 3 will still remain unmoved in an axial direction, and hencethe slot-width of the discharge-path between the two conical surfaceswill remain at itsminimum set value, so asto produce a maximumcurrentinterrupting ability as a result of the blast of un-ionized gasesor particles which are emitted by the Walls of the conical surfaces as aresult of their being subjected to the intimate play of the power-followarc thereagainst. The tube is thus enabled to interrupt the feeble arcswhich are produced by the lowest range of power-follow currents orshort-circuit currents of the protected line or apparatus, these smallpower-follow arcs being usually among those which are the most difiicultfor the tube to interrupt, because of the relatively small amount ofgas-evolution which is evoked by such weak arcs.

If, however, the tube should be applied on a line or apparatus in whichthe power-follow currents are very severe, such that thecurrentinterrupting limits of the tube are determined by theblasting-resisting strength of the tube, then the gaseous evolution isso strong as to develop a high gaseous pressure in the arcing pathbetween the two conical surfaces, and this gaseous pressure will developan axial component which moves the plug 3 man axial direction out of theconical opening 2,and against the yielding force exerted by the axiallyapplied compressionspring I6. It will be noted that the small angle orinclination of the conical walls results in the arc because of theirgreater separation. The

tube is thus protected against bursting, and this same solution isavailable also, in the event of extremely high-current surge-discharges.

As a further protection against bursting, the

pressure-relief valve 23 of the upper electrode can be provided andadjusted to become unseated in the presence of abnormalpressure-conditions, so as to vent the top end as well as the bottom endof the tube, in order to avoid a bursting or rupture of the tube.

The inner, arc-terminal depression 1 in the rod-like electrode 5 alsoserves as a gas-expansion chamber in which gas may flow or accumulate,until it builds up a pressure equal to the gaseous pressure in thenarrow slot between the two conical surfaces, thus also relieving theseverity of the gaseous-pressure conditions in the long, narrow slot.

In the event of an extremely severe surgecurrent on a protectedpower-line which has only a very small short-circuit current-value forproducing a power-follow current in the dischargetube, the plug 3 maymove radially outwardly with respect to the conical opening 2 during theheavy-current surge-discharge, after which the gaseous pressure withinthe tube will be reduced, because of the small power-follow current, sothat=the compression-spring l6 will returnthe plug 3*to its initialpositiomthus reducing the slot-width to the point where the tube caninterrupt the weak power-follow current.

7 'While I have illustrated and described my invention in a singleexemplary form of embodimen't, I wish it to be understood that saidexemplary form' is only by way of il1ustration,fiand not intended to beby way of limitation to this one precise form. I desire, therefore, thatthe appendedclaims'shall be accorded the broadest constructionconsistent with their language and the prior art.

I claim as my invention:

1. An excess-voltage protective device of the expulsion-tube type,comprising a tubular insulating structure having an opening which isconically enlarged at one end, a conical insulataxially into saidconical opening, at least one of the conical surfaces including materialcapable of evolving deionizing gases or particles under the influence ofan arc, the internal fiashovervoltage of the protective device beingless than ing opening a portion of which is conically shaped, a conicalinsulating plug, means for mounting said plug so that it has somecapability of longitudinal movement with respect to said tubularinsulating structure and including means for yieldably pressing saidconical plug axially into said conical opening, at least one of theconical surfaces including material capable of evolving delonizing gasesor particles under the influence of an arc, and a plurality ofpermanently separated and electrically insulated arcterminal electrodesso disposed, with at least one of said electrodes extending partway intothe tubular insulating structure, so that any electrical flashoverbetween said electrodes always results in a long, narrow dischargebetween said plug and said conical opening.

4. An excess-voltage protective device of the expulsion-tube type,comprising a tubular insulating structure having a. longitudinallyextendingopening a portion of which is conically shaped, a conicalinsulating plug, means for mounting said plug so that it has somecapability of longitudinal movement with respect to said tubularinsulating structure and including means for yieldably pressing saidconical plug axially into said conical opening and means for limitingthe extent to whch said plug is axially thrust into said conical openingso as to provide a long, narrow, slot-like separation of at least onesixtyfourth of an inch between said plug and said conical opening atleast one-of the conical surfaces including material capable of evolvingdeionizing gases or particles under the influence of an arc, and aplurality of permanently separated and electrically insulatedarc-terminal electrodes so disposedgwithat least one of said electrodesextending partway into the tubular insulating tructure, so/that anyelectrical'flashoverbetween said electrodes always results in a long,vnarrow discharge through said slot-like 10 acterized by means for soenclosing and venting the device that'an-electrical discharge resultsina gaseous blast flowing through the conical opening from the smaller tothe larger end thereof.

6. The invention as defined in claim 4, characterized by means for soenclosing and venting the device that an electricaldischarge results ina gaseous blast flowing through the conical opening from the smaller tothe larger end thereof.

ALERT M. 'OPSAHL.

